1. Field of the Invention
The present invention relates a method of separating iodine gas, and more particularly, the present invention relates to a method of separating iodine gas from a phase by passing a phase containing iodine gas through a membrane impermeable to iodine gas.
2. Description of the Related Art
Because hydrogen and oxygen are attracting attention as clean sources of energy, a method by which water is broken down electrochemically has been established for their production on an industrial scale. However, this method has problems in terms of cost since it requires a large amount of electrical power. In order to solve this problem, a method has been proposed for chemically decomposing water in Japanese Unexamined Patent Publication No. 55-21587 and Japanese Unexamined Patent Publication No. 8-301606.
Namely, as is represented by the following formula (1): EQU H.sub.2 O+X.sub.2 .fwdarw.HX+1/2O.sub.2 (1)
(wherein, X is a halogen), water is reacted with halogen to form hydrogen halide and oxygen by a chemical reaction, after which the hydrogen halide is electrically decomposed to form hydrogen. According to this method, since oxygen is obtained by a chemical reaction and hydrogen is obtained at a much lower voltage as a result of electrically decomposing hydrogen halide instead of electrically decomposing water directly, it offers the advantage of being able to reduce the amount of electrical energy required.
Although oxygen and hydrogen can be obtained at low cost with this type of method, there are problems in the step of isolating the oxygen and hydrogen halide from the reaction system containing halogen. Namely, since the pressure increases resulting in a dangerous situation, it is difficult for the reaction to proceed unless the formed gas is removed from the reaction system either continuously or in batches. However, since unreacted halogen is also contained in the reaction system in addition to the formed oxygen and hydrogen halide, it is necessary to remove only oxygen and hydrogen halide from the reaction system while continuing to hold the halogen in the system.
In the case of using bromine as the halogen, if a pipe that removes gas from the reaction system is cooled, although the water and bromine liquefy, the oxygen and hydrogen halide will remain in the gaseous state. Consequently, the formed oxygen and hydrogen halide can easily be separated from the bromine, allowing only gas to be removed. However, in the case of using iodine as the halogen, if a pipe for removing gas is cooled similar to the case of using bromine, since the melting point of iodine is 117.degree. C., the iodine solidifies and ends up clogging the pipe at a temperature at which water liquefies. In addition, even if a general gas separation membrane is used, iodine gas passes through this membrane, thereby not being separated from the oxygen and hydrogen halide.
In the case of using iodine as the halogen in the above-mentioned method of (1), since the resulting hydrogen iodide can be decomposed into hydrogen and iodine by heat alone without requiring electrical decomposition, it offers the advantage of having high thermal efficiency as a method of obtaining hydrogen. However, since it was not possible in the past to separate the oxygen, hydrogen halide and iodine gas as described above, the above-mentioned reaction of (1) could not be carried out continuously, but only in batches. Therefore, there is a need for a means of effectively separating iodine gas so that the above-mentioned method of (1) can be performed continuously.